1.Field of the Invention
The present invention relates to a free-piston Vuilleumier heat pump applicable to an air-conditioning system for the refrigeration or the heating and cooling of buildings and, more particularly, to the output control thereof.
2.Description of the Prior Art
FIGS. 15 and 16 are views showing the constitution of a prior art Vuilleumier heat pump and a simplified flow of output control processing disclosed in Japanese Patent Laid-Open No. Hei 2-4174. In FIG. 15, reference numeral 2 denotes a hot cylinder, in which a hot displacer 3, which separates a hot working space 2a hermetically filled with a high-pressure working gas such as helium from a moderate temperature working space 2b on the hot cylinder side, reciprocates. The hot working space 2a and the moderate temperature working space 2b on the hot cylinder side are connected through a hot heat exchanger 6, a regenerator 8 on the hot cylinder side, and a moderate temperature heat exchanger 9 on the hot cylinder side. The hot heat exchanger 6 is heated at the outer wall thereof by a heating device 36. Reference numeral 7 refers to a fin for accelerating heat exchange. Reference numeral 4 denotes a cold cylinder, in which a cold displacer 5, which separates a cold working space 4a from a moderate temperature working space 4b on the cold cylinder side, reciprocates. The cold working space 4a and the moderate temperature working space 4b on the cold cylinder side are connected through a cold heat exchanger 12, a regenerator 11 on the cold cylinder side, and a cold heat exchanger 10 on the cold cylinder side. Furthermore, the moderate temperature working space 2b on the hot cylinder side and the moderate temperature space 4b on the cold cylinder side are connected by a connecting pipe 14; on the outside wall of the cold heat exchanger 12 section, there is flowing a fluid which is circulated by the cooling water pump 38 between the heat exchangers 17 and 40 for cooling; and on the outside walls of the moderate temperature heat exchanger 10 on the cold cylinder side and the moderate temperature heat exchanger 9 on the hot cylinder side, a fluid which is circulated by a heating water pump 37 between the heat exchangers 15 and 39 for heating is flowing. The heat exchanger 39 for heating and a heat exchanger 40 for cooling are disposed outdoors, and the heat exchanger 15 for heating and a heat exchanger 17 for cooling are disposed in a room, thus constituting an indoor unit 41. Reference numeral 13 designates a tube; 16, a heating water pipe line; 18, a cooling water pipe line; and 42 to 45, three-way valves.
To the hot displacer 3 is fixedly connected a hot displacer rod 21; and to the cold displacer 5 is fixedly connected a cold displacer rod 22. The hot displacer rod 21 is mounted through a moderate temperature working space partition wall 26 on the hot cylinder side which has an appropriate sealing mechanism, and the cold displacer rod 22 is mounted through a moderate temperature working space partition wall 27 which has an appropriate sealing mechanism, and the rods are connected to a crank mechanism including members 19, 20 and 23 in the crank case 25. To a rotating shaft 24 of the crank mechanism are connected a driving device 28 and a braking device 29.
Next, operation will be explained by referring to a flowchart in FIG. 16. On starting, when a heat transfer medium such as water is circulated by the heating water pump 37 for the moderate temperature heat exchanger 9 on the hot cylinder side and the moderate temperature heat exchanger 10 on the cold cylinder side and by the cooling water pump 38 for the cold heat exchanger 12, for the purpose of thereby heating a part of the hot cylinder 2 and the surface of the hot heat exchanger 6 by use of the heating device 36 (Step ST2), and the driving device 28 is operated to reciprocate the hot displacer 3 and cold displacer 5 while maintaining a fixed phase difference (Step ST1). Then, the temperature of the working gas in the hot working space 2a rises and the temperature of the working gas in the moderate temperature working space 2b on the hot cylinder side rises a little higher than the temperature of a heat transfer medium which is circulated by the heating water pump 37, producing in the working gas a pressure change nearly proportional to the temperature difference between the working gas in the hot working space 2a and that in the moderate temperature working space 2b on the hot cylinder side.
Since the moderate temperature working space 2b on the hot cylinder side and the moderate temperature working space 4b on the cold cylinder side are connected by the connecting pipe 14, the pressure change of the working gas thus produced is transmitted, as it is, to the cold cylinder 4 side, and accordingly the temperature of the working gas in the moderate temperature working space 4b on the cold cylinder side is raised, by the work of compression of the working gas, nearly to the same temperature as the working gas in the moderate temperature working space 2b on the hot cylinder side. The temperature of the working gas in the cold working space 4a is decreased, by the work of expansion of the working gas, lower than that in the moderate temperature working space 4b on the cold cylinder side.
When the above-mentioned condition is obtained, the heat transfer medium circulated by the heating water pump 37 is heated by the working gas in the moderate temperature heat exchanger 9 on the hot cylinder side and the moderate temperature heat exchanger 10 on the cold cylinder side, thereby increasing in temperature to obtain the heat for heating a building. In the meantime, the heat transfer medium which is circulated by the cooling water pump 38 is cooled by the working gas in the cold heat exchanger 12, thus obtaining the heat for cooling a building.
A sufficient temperature rise of the working gas in the hot working space 2a produces a sufficient pressure change of the working gas; thus a pressure difference between the working gas on the cylinder side and the working gas on the crankcase 25 side acts on the hot displacer rod 21 and cold displacer rod 22, to generate a driving work, thus obtaining a self sustaining which does not require the driving device 28 at an operation frequency at which the driving work and a friction loss arising primarily in the mechanical section are balanced.
When an output necessary for a self-sustaining condition or more is required or when an output for the self-sustaining condition or less is required in accordance with a heating or cooling load, the following control is effected by a controller 32. First, information on the heating water temperature and cooling water temperature detected (Steps ST3 and ST5) by temperature detecting devices 30 and 31 for the heating effect transfer medium and the cooling effect transfer medium are compared with preset temperatures (Steps ST4 and ST6) in order to calculate a required speed (operation frequency) (Step ST7). Subsequently, the required speed and a self-sustaining operation speed are compared by use of a comparing device 33 (Step ST8). When the required speed is greater than the self-sustaining operation speed, a backup control of the driving device 28 is effected by means of a backup device 34 (Step ST9); and reversely when the required speed is less than the self-sustaining operation speed, a brake control of the braking device 29 is carried out by means of the brake control device 35 (Step ST10).
In the above-described prior art Vuilleumier heat pump, since the strokes of the displacers 3 and 5 in the cylinder per rotation of the crankshaft and a phase difference of the two displacers 3 and 5 are kept constant at all times, it is possible to control a heating or cooling energy output by changing the number of strokes of the displacers 3 and 5 per unit time, that is, the number of revolutions of the crankshaft, by controlling the driving device 28 or the braking device 29 mounted on the crankshaft end.
Next, a prior art free-piston Vuilleumier heat pump proposed by the applicant et al. in Japanese Patent Laid-Open No. 5-231735 that uses springs to constitute a resonance system shown in FIG. 17 will be explained. In FIG. 17, wherein parts corresponding to those in FIG. 15 are designated by the same reference numerals, and will not be described. In FIG. 17, reference numeral 51 refers to a coil spring on the hot cylinder side with one end thereof secured on a spring case 50 on the hot cylinder side, and the other end secured on the hot displacer rod 21 and a motor coil 52a on the hot cylinder side. Around the motor coil 52a on the hot cylinder side are disposed a magnet 52b on the hot cylinder side and a yoke 52c on the hot cylinder side as a magnetic circuit, thereby constituting a direct-acting motor 52.
Similarly, reference numeral 54 denotes a coil spring on the cold cylinder side, with one end thereof secured on a spring a spring case 53 on the cold cylinder side and the other end secured on a cold displacer rod 22 and a motor coil 55a on the cold cylinder side. Around the motor coil 55a on the cold cylinder side are disposed a magnet 55b on the cold cylinder side and a yoke 55c on the cold cylinder side as a magnetic circuit, thereby constituting a double-acting motor 55.
Next, operation of the heat pump will be explained. In the prior art example shown in FIG. 15, the hot displacer 3 and cold displacer 5, connected by the crank mechanisms 19, 20 and 23, are so constituted as to always maintain a constant phase difference and a stroke, while the hot displacer 3 and cold displacer 5 in the prior art example shown in FIG. 17 are constituted of resonance systems including independent springs 51 and 54, and they differ from the displacers in FIG. 15 in the respect that the phase difference and stroke of them vary according to operating conditions; however, their modes of operation on the cooling cycle are the same.
When the hot heat exchanger 6 is heated by the heating device 36, and one or both of the motor 52 on the hot cylinder side and the motor 55 on the cold cylinder side are started to reciprocate the hot displacer 3 and cold displacer 5, there occurs a pressure change with the movement of the working gas in the working space in the similar manner as the prior art example shown in FIG. 15. At this time, because of the presence of a pressure difference between the working gas within the working space and the working gas within the spring case 50 on the hot cylinder side, a driving force which is proportional to the sectional area of the hot displacer rod 21 acts on the hot displacer 3. The hot displacer 3 is driven by the resonance system utilizing this driving force and the restoring force of the coil spring 51 on the hot cylinder side; in a steady state, the reciprocating operation is repeated at an operation frequency, which is determined by both the resonance frequency of the driving system of the hot displacer 3 and the resonance frequency of the driving system of the cold displacer 5, even when the motor is stopped. At this time, with the movement of the working gas, the fluid resistance occurring in the hot heat exchanger 6, the regenerator 8 on the hot cylinder side and the moderate temperature heat exchanger 9 on the hot cylinder side and the sliding resistance by the sealing member (not shown) acts on the hot displacer 3 as a damping resistance which cancels the driving force, thereby determining the stroke.
In the meantime, the cold displacer 5 is similarly driven by the resonance system inclusive of the driving force proportional to the sectional area of the cold displacer rod 22 and the restoring force of the coil spring 54 on the cold cylinder side; the fluid resistance occurring at the moderate temperature heat exchanger 10 on the cold cylinder side, the regenerator 11 on the cold cylinder side, and the cold heat exchanger 12 and the sliding resistance caused by the sealing member (not shown) act as the damping resistance, thereby determining the stroke.
In the free-piston Vuilleumier heat pump, the optimum phase difference of the reciprocating motion between the hot displacer 3 and the cold displacer 5 is about 90 degrees because of the characteristics of gas cycle; therefore, in the case of the heat pump which is driven by use of a crankshaft as in the prior art example shown in FIG. 15, the crank angle has been pre-adjusted so as to provide the aforementioned phase difference, and also in the case of the free-piston heat pump as in the prior art example shown in FIG. 17, the spring constant and the weight of a movable part have been adjusted.
The free-piston Vuilleumier heat pump, being of the aforesaid constitution, has the following problem when the heating energy or cooling energy output is adjusted. That is, in the prior art Vuilleumier heat pump shown in Fig. 15, the two displacers 3 and 5 continue constant operation with a fixed phase difference even when the shaft speed is changed by means of the crank mechanism that has been pre-adjusted. FIG. 18 illustrates results of the heating energy and cooling energy outputs, the phase difference between the two displacers 3 and 5, and a coefficient of performance (COP) in the case of the free-piston type that the inventor et al. have acquired by experiments when the operation frequency corresponding to the crankshaft speed is changed. As these results indicate, the phase difference of the two displacers 3 and 5 varies in accordance with the change of the operation frequency; the heating energy and cooling energy outputs and the coefficient of performance at the resonance frequency (around 17.5 Hz in this example) which is determined by the driving system become a maximum; and if the operation frequency is deviated from the resonance frequency, the heating energy and cooling energy outputs and the coefficient of performance will be considerably deteriorated. Furthermore because the output characteristics vary at the resonance frequency, the output control will become complicated, making it necessary to change over the control between a higher required operation frequency than the resonance frequency and a lower required operation frequency than the resonance frequency and consequently resulting in difficult keeping of a stabilized condition of control.